The present invention relates to photosensitive alarm systems and, more particularly, to photosensitive intrusion detectors operable upon exposure to ambient light for protection of cash drawers, file cabinets, and shipping or storage containers.
In the handling of cash, checks, and other negotiable instruments at commercial installations such as banks, hotels, department stores and other business establishments, it is important to protect the cash drawers and other storage areas used to store the money, checks and negotiable instruments from unauthorized intrusion. Similar concerns apply to file cabinets and storage containers in which important documents, records, and other valuable items are stored and shipping containers used for shipment of valuable products.
A photosensitive alarm system which operates upon exposure to ambient light is particularly suitable for protection of such cash drawers, file cabinets, and storage or shipping containers. Preferably, the system becomes armed when placed in darkness in the storage area and is subsequently triggered when the storage area is exposed to ambient light.
Where a photosensitive alarm system is intended to provide protection for extended time periods, it is extremely desirable for the system to have the capability of recording the number of unauthorized intrusions and the time and date of the initial intrusion. For example, in the case of a cash drawer or file cabinet, it may be necessary to protect the drawer or cabinet against unauthorized intrusion overnight and on weekends. It may also be desirable to monitor the cash drawer or file cabinet during normal business hours.
In the case of a storage or shipping container, it may be necessary to provide protection over an even longer time period, e.g., several weeks or months. Consequently, it is essential for the photosensitive alarm system to have minimal power supply requirements when it is not exposed to the ambient light to allow the system to remain activated for long periods of time. This requirement is especially critical for battery operated alarm systems which must have long shelf life.
Moreover, the provision of an alarm system which records the time and date of the initial intrusion is especially desirable for storage or shipping containers intended to remain closed for long time periods. The time and date recorded helps to identify the party in possession of the container at the time the intrusion occurred. Where a plurality of storage or shipping containers require protection, it is desirable to employ an alarm system capable of transmitting unique identification signals to identify the specific container at which the intrusion occurred.
Various types of photosensitive alarm systems have been developed in the prior art which respond to ambient light to generate alarm signals. See, for example, U.S. Pat. No. 3,930,249 disclosing a photocell actuated wallet alarm which responds to ambient light upon removal of the wallet from a pocket or purse to generate an audible alarm signal. U.S. Pat. No. 3,909,819 discloses a mailbox alarm incorporating a photocell located inside a mailbox for sensing ambient light when the door of the mailbox is opened to activate an alarm at a remote location. The alarm serves to inform a homeowner of a mail delivery and remains activated until it is reset by the homeowner. Photosensitive monitoring systems are also known in which light is continuously shined upon a photocell and an alarm is activated upon interruption of the light. See, for example, U.S. Pat. Nos. 2,980,223; 3,750,157 and 3,786,460.
In addition, as demonstrated in U.S. Pat. No. 3,886,352, it is known to incorporate photocells in an automatic light control system which respond to automobile headlights to automatically switch on the lights in a garage or carport. The system includes a daylight sensor photocell to prevent operation of the system during daylight hours. The headlight sensing photocell and daylight sensing photocell are connected in a variable voltage divider which provides a sufficient potential, when darkness turns the daylight photocell off and headlights turn the headlight photocell on, to break down a zener diode to activate a gate and timer circuit to turn on the garage lights for a predetermined time. However, the voltage divider tends to draw a significant amount of current even when the control system is deactivated.
German Pat. No. 2,238,085 discloses an intruder alarm system consisting of two photoelectric detectors. The first detector is provided with a millisecond feedback and a high frequency limiter so that neither very slow nor very rapid changes in illumination result in an alarm signal. The second detector is a flicker detector which eliminates interference by automobile headlights or voltage fluctuations. A delay unit allows authorized personnel to enter the room to switch off the system without initiating an alarm signal.
None of the above references contemplate a battery powdered photosensitive alarm system incorporating separate photocell operated arming and trigger circuits designed to have minimal power requirements. Moreover, none of the references contemplate a photosensitive alarm system capable of detecting multiple intrusions, recording the number of intrusions, and providing alarm signals indicative of the number of intrusions. Nor do these references disclose intrusion detection systems which record the time and date of the initial intrusions or which generate unique identification signals to specify the location where the intrusion occurred.